Wideband antenna device with extended ground plane in a portable device

ABSTRACT

An antenna device for a portable device has an antenna loop of conducting material to be connected to radio circuitry in the portable device. The antenna loop is positioned opposite a ground plane of a PCB. Also, the antenna device also comprises at least one battery, which is positioned in the extension of a first side of the PCB, and acts as an extension of the ground plane of the PCB.

RELATED APPLICATIONS

The present application is a 35 U.S.C. §371 national phase applicationof PCT International Application No. PCT/EP03/006109, having aninternational filing date of Jun. 11, 2003 and claiming priority toEuropean Patent Application No. 02013085.2, filed Jun. 13, 2002,European Patent Application No. 02018940.3, filed Aug. 26, 2002 and U.S.Provisional Application No. 60/407,886 filed Sep. 3, 2002, thedisclosures of which are incorporated herein by reference in theirentireties. The above PCT International Application was published in theEnglish language and has International Publication No. WO 03/107473.

FIELD OF THE INVENTION

The present invention relates to an antenna device for use in a smallportable device. More specifically, the invention relates to a widebandantenna having sufficient efficiency for meeting the requirements ofdifferent communications protocols. Also, the antenna reduces the powerconsumption of the small portable device so it can operate longer on asmall battery.

BACKGROUND OF THE INVENTION

Examples of a small portable device is e.g. a headset for wirelesscommunication through an antenna with a mobile communication apparatus,such as a mobile telephone, a Bluetooth device, or any portable orstationary electronic device. A small portable device is, as indicated,characterized in that it is small and light. Therefore, it is preferredif the antenna used in such a device is small, light, and efficient. Thesmall portable device may communicate using a communication protocol,such as the Bluetooth, the WLAN (Wireless Local Area Network), the UMTS(Universal Mobile Telecommunications System), or the GSM (Global Systemfor Mobile communications) protocol.

One example of an antenna for a small portable device is a monopoleantenna, which extends out of the product. Another solution is a PIFA(Planar Inverted F Antenna) antenna. However, there are severaldrawbacks of these antennas. To achieve sufficient bandwidth to meet therequirements of known communication protocols, e.g. according to above,the known antennas all need ground planes, which are too big to fit in asmall portable device.

There are a number of problems with the known prior art-antennas, whichmake them unsuitable for use in a small portable device.

Firstly, the size of the small portable device causes problems for theantenna design, as it entails limited battery capacity. This means thatthe antenna should have a high efficiency in order not to waste batterypower. Small antennas have lower efficiency than big antennas. As thedevice is small, the ground plane will also be small. An antennarequires a certain ground plane size to achieve a certain bandwidth,which is necessary for the antenna to be able to operate under aspecific communications protocol, which always requires a certainbandwidth.

Secondly, since cost is often important for a small portable device itis important that the antenna can be made cheaply, which is not alwaysthe case with the antennas known in the art.

Thirdly, because of the small nature of the small portable device, otherparts of the device will be very close to the antenna, which can have anegative influence on the antenna performance. Especially conductingmaterials like batteries, knobs or ESD (electrostatic discharge) meanscan have a very negative influence on the antenna performance.Therefore, the antenna has to work well in this environment, which isalso not possible with the antennas according to the known prior art.

SUMMARY OF THE INVENTION

Therefore, the object of the present invention is to provide an antennadevice, which is sufficiently small to fit in small portable devices andwhich has efficiency and bandwidth to meet requirements of known andfuture communications protocols.

The above objects are achieved by an antenna device for a portabledevice, which comprises a folded antenna loop of conducting materialhaving first and second ends to be connected to radio frequency (RF)circuitry and a ground plane of a PCB, respectively. Further, theantenna device comprises a ground plane extender positioned in theextension of a first side of the PCB. In one embodiment of theinvention, the antenna extender is at least one battery casing of abattery cell having a position to serve as an extension of the groundplane of the PCB.

The antenna loop comprises first and second connectors provided at asecond side of the PCB for connecting the antenna loop to the RFcircuitry and the ground plane of the PCB, respectively.

Further, the antenna loop comprises:

a first portion having a first and a second end, said portion extendingin a first direction along a third side of the PCB, the first end beingconnected to the RF circuitry of the PCB;

a second portion having a first and a second end, the first end of thesecond portion being connected to the second end of the first portion,said second portion extending in a second direction from the third sideof the PCB towards a fourth side of the PCB, which is opposite the saidthird side; and

a third portion having a first and a second end, the first end of thethird portion being connected to the second end of the second portionand the second end of the third portion being connected to the groundplane of the PCB, said third portion extending in the direction oppositeto said first direction along said fourth side of the PCB.

In one embodiment, the PCB of the antenna device is a multi layer PCBhaving one layer used as a dedicated RF ground plane, which also servesas the ground plane of the antenna device. The antenna loop ispositioned opposite a first or a second surface of the PCB.

The material of the antenna loop is any well conducting material, suchas metal. In an alternative embodiment, the antenna loop is provided asa U-shaped dielectric having the antenna shape etched into thedielectric. Still another embodiment is to provide the antenna loopinside the PCB as an element thereof.

Additionally, the antenna device may be provided with a bezel, which isconnected to the PCB, for fending off ESD (Electrostatic Discharges)discharges. The bezel extends from the third side of the PCB towards thefourth side of the PCB. Also, to improve ESD robustness, the antennadevice may be provided with bezel flanges connected to the ground planeof the PCB, which extends along the third and fourth sides of said PCB.

A further object of the invention is to provide an PCB comprising anantenna device, which is sufficiently small to fit in small portabledevices, and which has good performance to meet requirements ofcommunications protocols.

The above objects are achieved by a multi-layer printed circuit board(PCB) comprising an antenna device according to the above.

Finally, it is an object of the invention to provide a portablecommunication device having an antenna with good performance and beingsufficiently small to fit into a small portable device. The efficiencyof the antenna device should be high to keep the power consumption low.As should be noticed, it is a further important object of the antennaaccording to the invention to provide high bandwidth to meet saidrequirements of communication protocols.

A portable device comprising the antenna device according to aboveachieves the above objects. In one embodiment, the portablecommunication device is a headset.

An advantage of an antenna device according to the present invention isthat it is sufficiently small to fit into small portable devices andstill provides good efficiency and high bandwidth. Therefore, theantenna device can be adapted to meet requirements of several differentcommunications protocols. Also, as the PCB of the antenna device may bedecreased, the weight and the cost of the antenna device are alsodecreased.

Further preferred features of the invention are defined in the dependentclaims.

It should be emphasized that the term “comprises/comprising” when usedin this specification is taken to specify the presence of statedfeatures, integers, steps, components or groups thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred and alternative embodiments of the present invention will bedescribed in the following detailed disclosure, reference being made tothe accompanying drawings, in which:

FIG. 1 illustrates a small portable device embodied as a headset;

FIG. 2 shows a general embodiment of the antenna device according to theinvention;

FIG. 3 shows a second embodiment of the antenna device according to theinvention;

FIG. 4 shows a third embodiment of the antenna device according to theinvention;

FIG. 5 shows a mag-log diagram of a measurement made on a prototype ofthe embodiment of FIG. 3; and

FIG. 6 shows a Smith chart of a measurement made on a prototype of theembodiment of FIG. 3.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In FIG. 1 is a small portable communication device illustrated as aheadset 1, which is adapted for wireless communication with a mobiletelephone 2. The small portable device could be any electroniccommunication device, which has to be small to meet user preferences andwhich is adapted to communicate wirelessly with another communicationdevice, which may be stationary or portable.

In the following, reference will be made to a headset 1 and a mobiletelephone 2. However, this is only for convenience and the illustratedheadset 1 and mobile telephone 2 are only for exemplifying purposes andshould not be taken as limiting the scope of the invention.

The headset 1 comprises a microphone 3 and a loudspeaker 4, throughwhich a user of the headset 1 may receive and transmit speech to themobile telephone 2 through a wireless connection 5. Also, it is equallypossible to communicate any data between the small portable device andthe mobile telephone 2.

In FIG. 2 a first general embodiment of an antenna device 10 accordingto the invention is shown, which may be positioned in the proximity ofthe loudspeaker 4 of FIG. 1. The antenna device 10 comprises a half-wavefolded antenna loop 11 having first 12, second 13, and third 14portions, respectively, each having a first and a second end. A firstconnector 15 a is connected to the first end of the first portion 12,and a second connector 15 b is connected to the second end of the thirdportion 14. The first end of the second portion 13 is connected to thesecond end of the first portion 12, and the second end of the secondportion 13 is connected to the first end of the third portion 14. InFIG. 2, the antenna loop 11 is provided opposite a first front surfaceof the PCB 16. However, the antenna loop 11 may equally be positionedopposite a second rearwardly facing surface of the PCB 16.

The antenna loop 11 is connected, through the connectors 15 a, 15 b, toradio circuitry and a ground plane within the PCB 16, respectively. ThePCB 16 can be made out of any known PCB, as long as one layer is used asa dedicated RF (Radio Frequency) ground plane, which also serves as theground plane of the antenna device 10. The connectors may be a part ofthe antenna loop 11 connected to the PCB 16 via holes provided in thePCB. The connectors may be provided at an angle α in relation antennaloop 11 and the PCB 16. This will shorten the total length of theantenna device compared to if the angle α is 90°. If the connectors areprovided essentially perpendicular to the PCB 16, the total length ofthe antenna is longer. However, if the connectors are folded with theangle α the antenna solution is made shorter without effecting theantenna performance.

Batteries 17 a, 17 b are positioned at a first side of the PCB 16. Theposition of the batteries 17 a, 17 b in relation to the PCB 16 and theconnectors 15 a, 15 b is important for the performance of the antennadevice 10, as will be further explained below. In FIG. 2, two batteries17 a, 17 b are shown. However, any suitable number of batteries may beutilized, depending on the actual configuration. The batteries 17 a, 17b can be of any configuration, technology or size suitable with theheadset 1, as long as they are provided in a battery casing.

The antenna device 10 is a loop antenna, wherein the antenna loop 11 ismade out of a metal, such as copper. However, any well conductingmaterial can be used. As an alternative embodiment, the antenna loopcould be provided as a loop on one layer of a multi-layer PCB 16. Stillanother embodiment is to provide the antenna loop 11 as a componentformed as a U-shaped dielectric with the antenna loop etched into it(like a thick PCB), making it suitable for SMT (Surface MountedTechnology) pick and place machines. As is shown in FIG. 2, the firstconnector 15 a is connected to the PCB at a second side thereof, whichis opposite the first side of the PCB 16.

The first portion 12 extends along a third side of the PCB 16 towardsthe first side of the PCB. The second portion 13 extends from the secondend of the first portion 12 towards a fourth side of the PCB 16.Finally, the third portion 14 extends from the second end of the secondportion 13 along the fourth side of the PCB 16 towards the secondantenna connector 15 b, which is connected to the PCB 16 at the secondside thereof.

The shape of the antenna loop 11 is not fixed, as can be seen from asecond embodiment shown in FIG. 3. Like numerals of FIG. 3 correspond tolike numerals of FIG. 2. Consequently, the antenna connectors 15 a, 15 bof FIG. 2 correspond to antenna connectors 25 a, 25 b of FIG. 3, theantenna loop 11 of FIG. 2 corresponds to an antenna loop 21 of FIG. 3etc. As is illustrated in FIG. 3, the angle between the first portion 22and the second portion 23, respectively, is less than 90 degrees. Thesame applies for the angle between the second and third portions 23, 24.However, the angles may be more than 90 degrees (not shown). Further,the first 23 and third 24 portions do not have to be straight, but canbe folded. Consequently, the exact design of the antenna loop 11, 21 isnot fixed, and has to be thoroughly tested and evaluated in eachspecific case.

The second embodiment of the antenna device 20 shown in FIG. 2 comprisesa bezel 28. The bezel 28 is provided between the antenna loop 21 and thebatteries 27 a, 27 b, and is connected to the PCB 26. The bezel 28 isoptional and utilized for fending off ESD (Electrostatic Discharge)discharges. The bezel extends from the third side of the PCB 26 towardsthe fourth side of the PCB 26. In the second embodiment it is made of ametal sheet, but can be made of any well conducting material.

In FIG. 4 a third embodiment of the invention is shown. Like numerals inFIG. 4 correspond to like numerals of FIG. 2 according to the samepattern as was described in relation to FIG. 3. In the third embodiment,the bezel 38 is provided with bezel flanges 39 a, 39 b extending alongthe third and fourth sides of the PCB 36. The bezel flanges 39 a, 39 bare, via the bezel 38, also connected to the PCB 36 and improves ESDrobustness without influencing the antenna performance negatively. Asshould be noticed, the bezel flanges 39 a, 39 b may be provided withoutthe bezel 38.

To extend the ground plane of the PCB 16, 26, 36 a ground plane extenderis provided in the extension of the first side of the PCB. Any wellconducting material will function as the extender. The battery cellprovided in a battery casing made of a conducting material, such asmetal, may provide the ground plane extender. Consequently, thebatteries 17 a, 17 b, 27 a, 27 b, 37 a, 37 b will act as an extension ofthe ground plane of the PCB 16, 26, 36 if they are positioned in theextension of the first side of the PCB 16, 26, 36, which is opposite thesecond side where the connectors 15 a, 15 b, 25 a, 25 b, 35 a 35 b areconnected to the PCB 16, 26, 36.

The position of the at least one battery 17 a, 17 b, 27 a, 27 b, 37 a,37 b is important for the antenna performance. Although the batteries 17a, 17 b, 27 a, 27 b, 37 a, 37 b are not directly connected to the groundplane of the PCB 16, 26, 36 they will act together with the ground planeof the PCB to form an extended ground plane, which is larger than theactual ground plane of the PCB. Therefore, the antenna loop 11, 21, 31will experience a ground plane which is sufficiently large withoutactually providing a ground plane having an actual size to achieve acertain bandwidth to meet requirements of a certain communicationsprotocol. Consequently, the PCB 16, 26, 36 may be decreased if thebatteries 17 a, 17 b, 27 a, 27 b, 37 a, 37 b are provided in a positionfor extending the ground plane. Therefore, the dimensioning of theantenna and the small portable device can be made small, and light.

The distance d between the PCB 16, 26, 36 and the batteries 17 a, 17 b,27 a, 27 b, 37 a, 37 b is approximately about 1 mm in the shownembodiments. However, the distance d has to be tested and evaluated ineach specific case.

A further tuning parameter of the antenna device 10, 20, 30 is that theconnectors 15 a, 15 b, 25 a, 25 b, 35 a 35 b should preferably beprovided as close as possible to the edge of the second side of the PCB16, 26, 36. The closer the connectors 15 a, 15 b, 25 a, 25 b, 35 a 35 bare to the edge of the second side of the PCB 16, 26, 36, the morebandwidth is gained. Similarly, the first and second portions 12, 22,32, 13, 23, 33 of the antenna loop, respectively, should preferably beprovided as close as possible to the third and fourth side of the PCB16, 26, 36, respectively. The closer said portions are to the third andfourth sides of the PCB, the more bandwidth is gained.

The antenna design according to the invention is sufficiently efficientto be adapted for communicating according to several protocols, such asBluetooth, WLAN, GSM, UMTS, ISM etc. There are a number of tuningparameters for adapting the antenna to a specific protocol, such as thelength of the antenna loop 11 (half wave antenna loop), the length L1 ofthe first and third portions 12, 14, respectively, the length L2 of thesecond portion 13, the length L3 and width W1, W2 of the PCB 16, thelength L4 and width W3 of the batteries 17 a, 17 b, the height H of theantenna loop 11 above the PCB 16, the distance D between the connectors15 a, 15 b, the thickness T of the antenna loop 11, the distance dbetween the PCB 16 and the batteries 17 a, 17 b, the angle α between thefirst and third portions 12, 14 and the connectors 15 a, 15 b, as isindicated in FIG. 2.

A preferred thickness of the antenna loop is about 0.1-1 mm.

The embodiment shown in FIG. 3 is adapted for communication according tothe Bluetooth protocol, wherein the center frequency is around 2,4-2,5GHz, and has the following approximate dimensions:

L1 22 mm L2 13.4 mm L3 38 mm L4 20 mm W1 10 mm W2 16 mm W3 16.5 mm(together) D 7.5 mm T 0.1-1 mm W4 2.3 mm H 5.1 mm d 1 mm α 50°

In FIG. 5 a log-mag diagram and in FIG. 6 a Smith chart of a measurementmade on a prototype of the embodiment of FIG. 3 are shown. Themeasurement is made with a human body behind the antenna device in orderto make the measurement as realistic as possible. From FIG. 5 and FIG. 6of a measurement made on a prototype of the embodiment of FIG. 3 it canbe concluded that the antenna device shows good performance, meeting thebandwidth requirements of the Bluetooth protocol.

If the height H is increased, bandwidth is gained. However, with anincreased height H the antenna will be more sensitive to theenvironment, such as the microphone 3, the loudspeaker 4, the user ofthe headset 1, and other electronic components of the headset, and viceversa. Also, in alternative embodiments the first, second and thirdportions of the antenna loop may be provided in different planes. Eachportion can be provided in a different plane if preferred.

As should be noted, the antenna has an input impedance of 50 ohm, andtherefore no impedance matching circuits are needed to match the antennato the RF circuitry of the PCB.

The present invention has been described with reference to a fewalternative embodiments. However, the embodiments are only forexemplifying purposes and should not be taken as limiting the scope ofthe invention, which is best defined by the appended independent claims.All dimensions of the antenna device according to the invention have tobe thoroughly tested and evaluated in each specific case. Further, theinvention has been described in relation to a headset. However, theinvention can be adapted to and utilized in any small portable device.Also, the antenna device can be used in other portable devices, such asmobile telephones, mobile terminals, smartphones, or the like, where asmall and efficient antenna design is preferred.

1. An antenna device for a portable device, the antenna devicecomprising an antenna loop of conducting material having first andsecond ends connected to a radio frequency (RF) circuitry and a groundplane of a printed circuit board (PCB), respectively, the antenna loopbeing positioned opposite the ground plane; and a ground plane extenderpositioned at a first side of the PCB and in a longitudinal extension ofthe ground plane, wherein the ground plane extender is a separate pieceand spaced apart a distance from the ground plane.
 2. The antenna deviceaccording to claim 1, wherein the antenna loop comprises first andsecond connectors provided at a second side of the PCB configured toconnect the first and second ends of the antenna loop to the REcircuitry and the ground plane of the PCB, respectively.
 3. The antennadevice according to claim 2, wherein the antenna loop further comprises:a first portion having a first and a second end, the first portionextending in a first direction along a third side of the PCB, the firstend of the first portion being connected to the RF circuitry of the PCB;a second portion having a first and a second end, the first end of thesecond portion being connected to the second end of the first portion,the second portion extending in a second direction from the third sideof the PCB towards a fourth side thereof, which is opposite the thirdside; and a third portion having a first and a second end, the first endof the third portion being connected to the second end of the secondportion and the second end of the third portion being connected to theground plane of the PCB, the third portion extending in the oppositedirection of the first direction along the fourth side of the PCB. 4.The antenna device according to claim 1, wherein the PCB is amulti-layer PCB having one layer configured as a dedicated RF groundplane that provides the ground plane of the antenna device.
 5. Theantenna device according to claim 4, wherein the antenna loop isprovided inside the PCB.
 6. The antenna device according to claim 1,wherein the ground plane extender is at least one battery casing of abattery cell, the at least one battery casing being positioned in thelongitudinal-extension of the ground plane of the PCB.
 7. The antennadevice according to claim 1, wherein the antenna loop is positionedopposite a first or a second surface of the PCB.
 8. The antennaaccording to claim 7, further comprising a U-shaped dielectric havingthe antenna loop-etched into the dielectric.
 9. The antenna deviceaccording to claim 1, wherein the conducting material of the antennaloop is metal.
 10. The loop antenna device according to claim 1, whereinthe ground plane extender is a battery casing.
 11. The loop antennadevice according to claim 1, wherein the first and second ends of theantenna loop comprise a planar portion configured to directly contactthe radio frequency (RF) circuitry and the ground plane of the printedcircuit board (PCB).
 12. The loop antenna device according to claim 1,wherein the first and second ends of the antenna loop are directlyconnected to the radio frequency (RF) circuitry and the ground plane ofthe printed circuit board (PCB).
 13. The loop antenna device accordingto claim 1, wherein the ground plane extender is not in direct contactwith the ground plane of the printed circuit board (PCB).
 14. The loopantenna device according to claim 1, wherein the ground plane extenderand the ground plane of the printed circuit board (PCB) together form anextended ground plane that is larger than the ground plane of theprinted circuit board (PCB).
 15. The loop antenna device according toclaim 1, wherein the first and second ends of the antenna loop areconnected to the printed circuit board (PCB) at a second side thereofthat is opposite the first side of the PCB and the ground planeextender.
 16. The loop antenna device according to claim 1, wherein thedistance between the ground plane extender and the ground plane is about1 mm.
 17. An antenna device for a portable device, the antenna devicecomprising an antenna loop of conducting material having first andsecond ends connected to a radio frequency (RE) circuitry and a groundplane of a printed circuit board (PCB), respectively, the antenna loopbeing positioned opposite the ground plane; and a ground plane extenderpositioned at a first side of the PCB and in a longitudinal extension ofthe ground plane, wherein the PCB further comprises a second sideopposite the first side, a third side adjacent the first and secondsides, and a fourth side opposite the third side, the antenna devicefurther comprising a bezel connected to the PCB that extends from thethird side of the PCB towards the fourth side of the PCB, and/or bezelflanges connected to the ground plane and extending along the third andfourth sides of the PCB.
 18. A multi-layer printed circuit board (PCB)comprising: a radio frequency (RF) circuitry and a ground plane on thePCB; an antenna device connected to the PCB, the antenna devicecomprising: an antenna loop of conducting material having first andsecond ends connected to the radio frequency (RF) circuitry and theground plane of the PCB, respectively, the antenna loop being positionedopposite the ground plane; and a ground plane extender positioned at afirst side of the PCB and in a longitudinal extension of the groundplane, wherein the ground plane extender is a separate piece and spacedapart a distance from the ground plane.
 19. A portable communicationdevice comprising: a printed circuit board (PCB) comprising a radiofrequency (RF) circuitry and a ground plane; an antenna device connectedto the PCB, the antenna device comprising: an antenna loop of conductingmaterial having first and second ends connected to the radio frequency(RE) circuitry and the ground plane of the PCB, respectively, theantenna loop being positioned opposite the ground plane; and a groundplane extender positioned at a first side of the PCB and in alongitudinal extension of the ground plane, wherein the ground planeextender is a separate piece and spaced apart a distance from the groundplane.
 20. The portable communication device according to claim 19,wherein the portable communication device is a headset.